The present invention relates to a device and to a method for detecting an impact on a composite material structure.
Composite materials are widely used in aeronautics, including for making the elements of the primary structure of the aircraft constituting the fuselage.
During a flight, or while the aircraft is being parked, these exterior structural elements are apt to undergo diverse impacts.
It is therefore necessary to undertake a check of these exterior structural elements regularly, and preferably before each new use of the aircraft.
This check is performed by searching for any damage due to impacts on these structural elements.
Since this check has to be performed on all these elements, it is lengthy and tedious.
Moreover, it is not sufficient to carry out a visual check of these structural elements.
Indeed, a composite material structure that has received an impact may be damaged inside, for example by delamination, while exhibiting an exterior aspect similar to that of an intact structure.
Hence, in the case of suspicion of damage and periodically, provision is generally made for an ultrasound-based check on the integrity of the exterior structural elements, this type of conventional check making it possible to detect damage inside a composite material structure.
According to a first drawback, this conventional ultrasound-based check remains a lengthy and tedious operation, the emitting probe having to be moved over all the exterior structural elements to be checked.
Moreover, certain zones of these exterior structural elements are difficult to access and therefore difficult to check.
According to another drawback, for certain levels of impact energy, accidental delaminations remain invisible with these conventional non-destructive checking means.
Consequently, plies are added to the composite material structure during the design of these exterior structural elements so as to guarantee their resilience in the presence of defects that cannot be detected with conventional non-destructive checking means.
These additional plies increase the overall weight of the aircraft and penalize its performance.
Hence, a need exists for a device and for a non-destructive method making it possible to identify and to locate an impact in a composite material structure, and also making it possible to determine the energy level of the impact so as to evaluate its criticality.
Hence, an installation for detecting and analyzing the damage undergone by the fuselage of an aircraft while parked is known from patent FR-2,937,953.
More particularly, this installation is intended to monitor the opening of a door or of a hatch for access to the internal volume of the aircraft.
For this purpose, this installation comprises:                an array of sensors of the piezoelectric type installed around this opening on the internal face of the fuselage, and able to sense mechanical vibrations propagating in the structure of the fuselage around the opening and to produce electrical signals representative of the mechanical vibrations sensed,        a processing unit connected electrically by wire to the array of sensors, and able to ensure the recording of the electrical signals produced by the sensors and to digitally process them so as to detect a strike on the fuselage around the opening, and so as to determine whether this strike is damaging, and if such is the case, to locate the latter,        a local alarm situated near the door, connected electrically by wire to the processing unit and activated by the latter when the strike is damaging,        a data concentrator connected electrically by wire to the processing unit, the concentrator being able to collect the alarm data originating from the processing unit and to transmit them electrically by wire to a centralized display,        a centralized display intended to be connected electrically by wire to the data concentrator, able to display for each opening an alarm state, and if a damaging strike is detected, an item of information relating to the location of the strike.        
Generally, the installation which is described in this document FR-2,937,953 is not suited to the detection of an impact on a composite material structure since it has been developed for sheet metal aircraft fuselages.
Then, the installation disclosed in this document FR-2,937,953 is only intended to be active when the aircraft is on the ground and at rest. Therefore, it does not make it possible to detect impacts on the exterior structural elements when the aircraft is in flight.
Moreover, in the installation disclosed in this document FR-2,937,953, the sensors of the piezoelectric type are linked by wire to the processing unit, which is itself linked by wire to the data concentrator, itself connected by wire to a centralized display provided to be installed in the flight deck.
Consequently, the entirety of the detection installation must be integrated into the aircraft right from its design and its assembly, thereby preventing any use of this installation on existing aircraft, without dismantling numerous elements and providing numerous hours of labor.